We fool ourselves into thinking we NEED a faster language, and Hindley-Milner type checking, and everything else under the sun.
It's actually really hard to discover, whether you're fooling yourself or not here.
We're building our startup on Ruby/Rails with a clojure component for the speed sensitive stuff (which is actually a CPU bound number crunching affair). So far we're been very happy with the tradeoff. We tried building stuff in node, but the ecosystem is just so damn immature.
One of the nicest things about the Ruby community, that I haven't seen in any other language, is the cultural emphasis on good documentation. Java libs have very complete docs, that take forever and a day to read when you just want to use one damn feature, node.js projects have very pragmatic, but very incomplete docs, (same with clojure), and really, that's the case with most languages. Ruby on the other hand, seems to have instilled in its community that docs count, and its wonderful.
Rails testing and tooling is just ahead of the pack, and in the specific case of node, dealing with the irritation of async (inscrutable stacktraces, even when 'long' stacktraces are enabled, inconsistent uses of promises across libs, etc.), is a huge drag on productivity. If I needed a small highly concurrent component I'd consider it, but for general business logic Rails just kills it.